High voltage deflection correction in CRT displays

ABSTRACT

The X and Y deflection voltages for a CRT display are corrected to accommodate excursions in the acceleration or anode voltage of a CRT display by multiplication with a signal which is a function of the square root of the high voltage. The invention (may be practiced following pincushion correction (correction for a planar CRT screen geometry), or directly. A second embodiment) integrates pincushion and anode voltage correction, thereby to require fewer and simpler circuits.

United States Patent [191 Waehner et al.

[111 E Re. 28,631

[ Reissued Nov. 25, 1975 HIGH VOLTAGE DEFLECTION CORRECTION IN CRTDISPLAYS [75] Inventors: Glenn C. Waehner, Riverside,

Conn.; Thomas J. Ray, Yonkers, NY.

[73] Assignee: United Technologies Corporation,

East Hartford, Conn.

[22] Filed: Sept. 16, 1974 2|] App]. No.: 506,061

Related US. Patent Documents Primary Examiner-T. H. Tubbesing AssistantExaminer.l. M. Potenza Attorney, Agent, or FirmM. P. Williams [57]ABSTRACT The X and Y deflection voltages for a CRT display are Relssueof: corrected to accommodate excursions in the accelera- Patent3,713,001 tion or anode voltage of a CRT display by multiplica- ISSUedIJ 1973 tion with a signal which is a function of the square PP 219,465root of the high voltage. The invention [may be prac- Flledl 1972 ticedfollowing pincushion correction (correction for a planar CRT screengeometry), or directly. A second [52] US. Cl 315/371; 315/379embodiment] integrates pincushion and anode volt- [Sl] Int. CL: "01.29/70 age o tion thereby to require fewer and simpler [58] Field 0fSearch 315/370, 37], 379, 411; i i

1 Claim, 2 Drawing Figures 1 AMP HIGH VOLTAGE DEFLECTION CORRECTION INCRT DISPLAYS Matter enclosed in heavy brackets I: 1 appears in theoriginal patent but forms no part of this reissue specification; matterprinted in italics indicates the additions made by reissue.

BACKGROUND OF THE INVENTION Field of invention This invention relates tocathode ray tube deflection circuitry, and more particularly tocorrelation of deflcction voltages with anode voltage excursions.

Description of the prior art As is known in the art, the extent to whichthe beam of electrons in a cathode ray tube is deflected by deflectionvoltages is highly dependent upon the energy, or velocity, of the beam,which in turn is a function of the accelerating voltage applied to theanode of the CRT.

A recent addition to the cathode ray tube art is the multiple phosphor,variable penetration type of tube. One such tube comprises a multi-colortube in which phosphors that emit different colors in response tobombardment by electrons are arranged in layers, a first layer (closerto the gun of the CRT) excited by lower energy electrons and a secondlayer (further from the gun ofthe CRT) being separated therefrom by anenergy barrier excited by higher energy electrons. Low anode voltagesexcite only the first phosphor (which may typically be red), whilehigher anode voltages (causing increasing beam energy) also excite asecond phosphor (which may typically be green). Since the human eye ismore sensitive to the green than to the red, and since it is moreefficient than is the red, high energy bombardment gives a definite,bright (although not pure) green color while low energy bombardmentgives a definite (though not pure) red color. In addition, energiesbetween the two can provide apparent various shades of orange andgreenish yellow, so that as many as four or five clearly discerniblecolors may be achieved with some of the more sophisticated penetrationtype color tubes now available.

In order to create displays in a plurality of colors, it is necessary toactivate the different colors at a sufficiently rapid rate so as tocreate the appearance of a steady display to the eye. Typically,generation of all the symbols of one color may be followed by all thesymbols of another color, and a third, etc., repetitively in a cyclicfashion. Thus, the anode voltage must be slewed between differentcolor-producing levels at sub video rates (for instance, the anodevoltage may have to change by several kilovolts every five or tenmilliseconds). Slewing of the anode voltage requires that the deflectionvoltages be altered suitably so as to provide the desired deflectionwithout regard to the desired color.

In the prior art, correlation of deflection voltage with the anodevoltage has typically been achieved by utilizing different fixedresistor networks which are switched in and out at sub-video rates toaccommodate the different anode voltages during generation of differentcolor portions of the display. However, this requires that the anodevoltage, at each color-selecting level, be

held to very close tolerances since a very minor change in anode voltagewill result in a different size picture in one color in contrast withanother which causes different color segments of the same display to beof different sizes and at misregistered locations. Furthermore, the rateat which video can be generated is limited by the need to allow theanode voltage to settle down (stop ringing) after switching from onevoltage to another in each case. Further, there is a dependence upondiscrete anode voltages (due to the need to utilize switched-in, fixedparameters), which precludes instantaneous control over color, andrenders it difficult to provide multi-color section in a two-phosphortube.

SUMMARY OF INVENTION The object of the present invention is to provideautomatic correlation between anode voltage and deflection voltage in aCRT display.

According to the present invention, the deflection voltages applied to aCRT display are correlated to the anode voltage by being amplified witha gain which varies as a function of the square root of the anodevoltage In accordance with the invention in one form, .anode correlationmay be achieved alone; in accordance with the invention in another form,anode correlation may be achieved on deflection voltages which alreadyhave correction for pincushion (or geometry) distortion applied thereto.In further accord with the present invention, anode correlation isprovided together with CRT geometry distortion correction in anintegrated deflection correction and correlation channel which utilizesfewer and simpler components.

The present invention provides automatic correlation of CRT deflectionvoltage with its anode voltage. Since it is automatic, there is no needto accurately control the voltage of the anode power supply.Additionally, the voltage may be readily adjusted, not only in steps toprovide different phosphor penetration (such as in multi-phosphor,variable penetration color tubes), but also permits free and easyadjustment of the anode supply so as to vary the hues of colors, orprovide similar functions in other displays. The invention eliminatesthe need for anode voltage monitoring and for switching of compensationcircuits at sub-video rates; and it is far simpler, less expensive andmore reliable than anode correlation circuits known to the prior art.

Other objects, features and advantages of the present invention willbecome more apparent in the light of the following detailed descriptionof preferred embodiments thereof, as illustrated in the accompanyingdrawmg.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a schematic block diagram ofa simple I embodiment of the present invention;] form of anodecorrection known to the arr and FIG. 2 is a schematic block diagram ofan embodiment of the present invention integrated with CRT ge ometrydistortion correction.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1 for ageneral understanding ofthe correction used herein, a cathode ray tube10 has an anode terminal 12 to which high voltage is applied on a line14 by a high voltage power supply I6. The CRT 10 has X deflectionvoltages applied thereto on a line I8 and Y deflection voltages appliedthereto on a 3 line from respective deflection amplifiers 22, 24 whichin turn are fed by related multipliers 26, 28. Each of the multipliers26, 28 is responsive to a signal on a line 30. which is a function ofthe square root of the anode voltage on the line I4. in response to asquare root circuit 32 which may take any one of sev eral forms. Forinstance, it may comprise a diode/resistor network of the general typeillustrated in a copending application of the same assignee entitled CRTGeometry Correction Network. Ser. No. 155,094, flied on June 21, l97l byV. G. Bello. now US. Pat. No. 3.825.796. Or. it may take the form of areciprocal exponential transconductance multiplier of the type disclosedin our copending application entitled Exponential TransconductanceMultiplier and Integrated Video Processor, [(UAC Docket No. N-694)l73Ser. No. 213.509, filed [in] on Dec. 2). I971 now U.S. Pat. No.3.793.480. On the other hand it may comprise a squaring feedbackmultiplier or any one of a plethora of other known circuits which canprovide the square root function. The multipliers 26, 28 are alsoresponsive to X and Y deflection signals applied thereto on relatedlines 34, 36 from a pair of inputs 38, 40. Thus there are rovidedl and Ydeflection signals =K.X V

where X is the X deflection signal as applied to the CRT Vis the Ydeflection signal as applied to the CRT K is a scalar constant X is theuncorrelated X deflection siganl at the input 38 and Y is theuncorrelated Y deflection signal at the input Thus, in the apparatus1040 of FIG. 1, there is disclosed a first embodiment of the presentinvention; that is deflection voltage amplifiers which correlate thedeflection voltage with the anode voltage in a CRT display system. Inthis embodiment of the invention, the deflection voltages applied to theinputs 38 and 40 may either be raw deflection voltage from the videosection of apparatus having information to be displayed on the CRT II].or they may comprise deflection voltages corrected for pincushion (CRTgeometry distortion) applied to the inputs 38, 40 by a pincushioncorrection circuit 42. The pincushion correction circuit 42, as shown inFIG. I, is a minor variation of that disclosed in US. Pat. 3.422.306 toS. B. Gray; if desired, it may take that form. or a more sophisticatedand accurate form as disclosed in the aforementioned copendingapplication of Belle.

In the form shown in FIG. 1, the pincushion correction circuit 42comprises four multiplier circuits 44-47 and a summing network 48.Because the multiplier 44 is assumed to be an inverting multiplier (or anoninverting multiplier followed by an inverter, if desired), andbecause both inputs of the summing network 44 are connected to a line 50which is responsive to raw X deflection voltages applied to a raw inputterminal 52 by the video source (not shown). it provides an output onthe line 54 which is equal to K)(. Similarly, the multi plier 45provides a signal on a line 56 equal to KY in response to raw Ydeflection voltages applied over a line 58 from a raw Y input terminal60. In addition to the signals on the lines 54, 56, the summing network48 has an input applied thereto from a terminal [62] 68 which is aconstant voltage suitably adjusted to be equivalent to unity in thegiven implementation of the present invention. This is achieved bysuitable choice of the scale factors, or gains, in the circuit, relativeto the voltage input at the terminal [62] 68 so that deflection givingthe sum (it y) equal to I: unity] zero will result in [no] unity outputfrom the summing network 48, as is well known in the art.

The output of the summing network 48 on a line 70 comprises a signalequivalent to lK x+y l (3) This signal is applied by a line 70 to themultipliers 46, 47 together with the raw X and raw Y deflectionvoltages, respectively, so as to provide CRT distortion corrected X andY deflection voltages on related signal lines 72. 74 as follows:

Y=yl |K,i x+yll 5) Equations 4 and 5 will be recognized by those skilledin the art as expressions for deflection voltages which have beenapproximately corrected for CRT distortion. By making K a nonlinearvariable, the more accurate correction of the Hello I application]parent may be achieved, as described therein. By substituting Equations4 and 5 into Equations l and 2 it can be seen that the actual deflectionvoltages achieved in the full cir- It should be understood that thegeometry distortion correction circuitry 42 forms no part of the presentinvention. but is described herein as an aid in understanding a secondembodiment of the invention in which anode correlation and geometrydistortion correction are integrated, as is illustrated in FIG. 2.

Referring now to FIG. 2, like elements performing the same function asin FIG. I bear the same reference numerals and will not be describedfurther. In FIG. 2, the summing network 483 does not have a constantinput thereto, so that its output on a line 76 comprises simply lent toThe signal on the line 80 is applied to a summing network 82 which isalso responsive to the anode voltage on the line 14 to provide a signalon a line 84 which is /\7 /'VK,(x+ 2) (to) Then. the multipliers 26, 28respond to the signal on the line 84 and to the respective signals onlines 50 and (Ill It can be seen that Equations 1 I and 12 are the sameas Equations 6 and 7. Thus. the circuit of FIG. 2 provides.

in an integrated fashion. the combined distortion correction and anodevoltage correlation as provided independently by the distortioncorrection circuit 42 and the remaining circuitry of FIG. I.

The multipliers 44, 45 must be four-quadrant multipliers since bothinputs may be either positive or negative. On the other hand. themultipliers 26, 28 and 46, 47 need only be two-quadrant multiplierssince the inputs thereto on lines 30 and 70, respectively, are alwayspositive and only the other inputs could be either positive or negative.The multipliers 78 in FIG. 2 need only be a single quadrant multipliersince both inputs are always positive. As is known, fewer quadrantsusually can be achieved in less expensive circuitry; thus, there is anadditional advantage to the circuit of FIG 2, in that it not onlyeliminates one multiplier compared to the total circuitry of FIG. I, butallows use ofa simpler one as well.

As mentioned hereinbefore, the [present invention anode correction maybe practiced without pincushion correction by using simply the apparatus-40 in FIG. 1, and not utilizing the pincushion (or geometry distortion)correction circuit 42 in FIG. 1, nor related apparatus in FIG, 2. Thismay be advantageous where space, cost or weight are critical factorssince the dependence of deflection on high voltage is a forty to fiftypercent effect. whereas the deflection correction is more like a tenpercent effect. This also means that the multipliers used only forpincushion correction need not be high quality, though it is preferablethat the multipliers used in anode correlation be of relatively highquality.

Although the invention has been shown and described with respect topreferred embodiments thereof, it should be understood by those skilledin the art that the foregoing and various other changes and ommissionsin the form and detail thereof may be made therein without departingfrom the spirit and the scope of the invention.

Having thus described typical embodiments of our invention, that whichwe claim as new and desire to secure by Letters Patent of the UnitedStates is:

II. A cathode ray tube display system comprising:

a cathode ray tube having a high voltage anode;

a high voltage supply connected to said anode and providing an anodevoltage thcrcto',

means responsive to said high voltage supply for generating a signal asa function of the square root of said anode voltage; and

means receiving X and Y deflection voltages in accordance with thatwhich is to be displayed on said cathode ray tube and responsive to saidsquare root means to provide deflection voltages to said cathode raytube which are functions of the respective products of said X and Ydeflection voltages with said square root signal] 2. In a cathode raytube display system receiving raw x and y deflection voltages to governdesired displays on the cathode ray tube, the deflection voltagemodificationn apparatus comprising:

a cathode ray tube having a high voltage anode;

a high voltage supply providing an anode voltage to the anode of saidcathode ray tube;

means responsive to said high voltage supply for providing a signal as afunction of the square root of said anode voltage;

sun [sunilmeans receiving raw x and y deflection voltage signals andproviding a negative scalar of the sum of the squares thereof;

means responsive to said sum means [,1 and said square root means [andsaid high voltage supply] for providing a signal which is a function ofsaid [anode voltage] square root signalminus the product of said squareroot signal and said negative scalar function of said sums of squaressignals; and means receiving said raw x and y deflection voltages andresponsive to said last named means for providing X and Y deflectionsignals to said cathode ray tube as respective products of the output ofsaid last named means and said raw deflection voltages.

PATENT NO.

DATED INVENTOR(S) 1 UNITED STATES PATENT OFFICE CERTIFICATE OFCORRECTION It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown beiow:

Column 2, line Column 2, line Column Column Column Column Column ColumnColumn Column Column [SEAL] line line

line

line

line

23, before In" insert (heavy bracket) 29, after "provided" insert "3(heavy bracket) 43, "voltage" should read --voltages-- 6, "Election"should read --flections-- Equation 7, line 34, "(x 2+y should read --x+y Equation 10, line 59, "(x +-2)" should read --x +y claim 2, line 20,

claim 2, line 27,

"cationn" should read --cation-- "sun rsunq" should read Signed andScaled this thirtieth D f March 1976 A nest:

RUTH C. MASON Arresting Officer

2. In a cathode ray tube display system receiving raw x and y deflectionvoltages to govern desired displays on the cathode ray tube, thedeflection voltage modificationn apparatus comprising: a cathode raytube having a high voltage anode; a high voltage supply providing ananode voltage to the anode of said cathode ray tube; means responsive tosaid high voltage supply for providing a signal as a function of thesquare root of said anode voltage; (sun) sum means receiving raw x and ydeflection voltage signals and providing a negative scalar of the sum ofthe squares thereof; means responsive to said sum means (,) and saidsquare root means (and said high voltage supply) for providing a signalwhich is a function of said (anode voltage) square root signal minus theproduct of said square root signal and said negative scalar function ofsaid sums of squares signals; and means receiving said raw x and ydeflection voltages and responsive to said last named means forproviding X and Y deflection signals to said cathode ray tube asrespective products of the output of said last named means and said rawdeflection voltages.